This application claims the benefit of Korean Patent Application No. 10-2004-0102964, filed on Dec. 8, 2004, and Korean Patent Application No. 10-2005-0042423, filed on May 20, 2005, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein in their entirety by reference.
1. Field of the Invention
The present invention relates to an optical transmission apparatus and method, and more particularly, to an optical transmission apparatus and method using a light source for wavelength division multiplexing (WDM) optical communication that employs a Fabry-Perot laser diode (F-P LD) whose output wavelength is locked by an externally injected incoherent light, a multifiber, and a waveguide grating router.
2. Description of the Related Art
Wavelength division multiplexing (WDM) optical transmission apparatuses are being introduced to satisfy increasing communication demands. In particular, WDM optical transmission apparatuses are being introduced into metropolitan networks and access networks that provide broadband services such as electronic commerce, cable TV, video conferencing, etc. necessary for a future information society.
FIG. 1 illustrates a conventional WDM optical transmission apparatus. A transmission node of the conventional WDM optical transmission apparatus includes N transmitters TX1-TXN that output optical signals λ1˜λN having different wavelengths, and an N×1 multiplexer MUX that multiplexes output signals of the N transmitters TX1-TXN. A reception node of the conventional WDM optical transmission apparatus includes a 1×N demultiplexer DEMUX that divides received signals into optical signals of different wavelengths, and N receivers RX1-RXN that regenerate electrical signals from the optical signals. The transmission node and the reception node are connected via an optical fiber. In case where a transmission distance is long, an optical amplifier is used to compensate for loss of the optical fiber.
Since channels for connecting the transmission node and the reception node of the conventional WDM optical transmission apparatus are divided by wavelengths of the optical signals, a light source used for the transmission node needs a stable output wavelength, and interference between adjacent channels needs to be minimized. The conventional WDM optical transmission apparatus needs high output power to guarantee a sufficient optical signal to noise ratio, and a narrow line width to minimize effect of chromatic dispersion. A distributed feedback laser diode (DFB LD) is a light source that meets such requirements. However, since the DFB LD is expensive, incoherent lights are usually used in the access network that requries an economical light source.
Since incoherent lights using a light emitting diode (LED), a super luminescent diode (SLD), and a natural emitting light of the optical amplifier have wide spectrums, it is difficult to use a WDM light source as it is, and a spectrum slicing method is used. However, the LED does not have sufficient output power to provide a plurality of channels using the spectrum slicing method, and while the SLD has relatively high output power it is expensive. The light source of the optical amplifier has high output power but needs an external modulator.
A light source for the WDM optical communication using a Fabry-Perot laser diode (F-P LD) whose output wavelength is locked by an externally injected incoherent light is an economical light source. Although it is economical, a plurality of users uses a plurality of light sources, i.e., different wavelengths.